In the manufacturing of thin film device products, thin film devices such as field effect transistors (FET), thin film transistors (TFT), light emitting diodes (LED), memory circuits, display circuits or optical devices are fabricated on a substrate through various processes such as chemical vapor deposition, etching, oxidation, and annealing. Since the fabrication processes often involve high temperature treatment, one of the substrate requirements is high temperature heat resistance, meaning the substrate must have a high softening temperature and a high melting temperature. To minimize film stress and maintain good alignment of different patterned layers, it should also have a low coefficient of thermal expansion and low distortion after thermal cycling.
Thin film transistor (TFT) processes for liquid crystal displays currently use quartz glass substrates to provide heat resistance up to approx. 1000° C., or heat-resistant glass substrate to provide heat resistance up to approx. 500° C. However, quartz and heat resistant glass substrates are expensive, heavy and fragile.
Low temperature thin film transistor processes on plastic substrate have been demonstrated, for example,                U.S. Pat. No. 5,742,075, “Amorphous Silicon on Insulator VLSI Circuit Structures” by Stanley G. Burns et al;        U.S. Pat. No. 5,796,121, “Thin Film Transistors Fabricated on Plastic Transistors”, by Stephen McConnell Gates, and        U.S. Pat. No. 5,817,550, “Method for Formation of Thin Film Transistors on Plastic Substrates”, by Paul G. Carey et al.,but in general, temperatures up to around 200–300° C. may be required to get good device performance as indicated by charge carrier mobility or low interface state density. Polymer substrates which can tolerate these temperatures do exist; for example, polyimides, poly(ether sulphone)s, polycarbonates, polyaramids. But these polymer substrates are often colored, very expensive, have high water absorbance and less than ideal thermal and mechanical properties.        
In contrast, the ideal product substrate is preferably as inexpensive as possible, light weight, transparent, resistant to deformation to a certain extent, and invulnerable to dropping. Thus there is a difference between the requirements of a substrate for fabrication processes and the characteristics desirable for a product substrate. It has been extremely difficult to satisfy both these required process conditions and desirable product characteristics.
The substrate transfer method can be used to address the above problems. The thin film devices are fabricated on a donor substrate having the desired optimal properties for fabrication processes in which the donor substrate has been first coated with a suitable releasable adhesion layer. Then the fabricated thin film devices are transferred to a target substrate (or a receptor) having the desired product characteristics. For example, see Wolk et al., U.S. Pat. No. 6,114,088, and its divisions, U.S. Pat. No. 6,221,553 and U.S. patent publication 2001/0036561, “Thermal transfer element for forming multilayer devices”, and Inoue et al., U.S. Pat. No. 6,521,511, “Thin film device transfer method, thin film device, thin film integrated circuit device, active matrix board, liquid crystal display, and electronic apparatus”.
However, the most difficult aspect of the substrate transfer method is the selection of the releasable adhesion layer. Currently to the best of our knowledge, there is no suitable releasable adhesion layer, one that can provide good adhesion during high temperature fabrication processing and at the same time can delaminate at a low temperature for transferring to a target substrate.